What does INR stand for?

• A. Prothrombin time
• B. International normalised ratio
• C. International ratio
• D. International normalised ratio test

Answer: (B)

INR stands for International Normalised Ratio. This is a standardized way to express the time it takes blood to clot, derived from the prothrombin time test but adjusted so results are comparable across different labs and reagent sensitivities. The “International” part reflects global standardization, and “Normalised” indicates adjustment for how reactive the thromboplastin reagent is (using the ISI). The result is used to monitor anticoagulation therapy, especially with warfarin, to keep the patient’s clotting tendency within a target range.

The other options miss key elements: the test name is prothrombin time, not the acronym itself; “International ratio” omits the normalization step; and adding “test” to the acronym isn’t part of the official name.